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Indirect Proof in Algebra and Geometry

Proof by contradiction.

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Contradictory Evidence

Credit: James Burke
Source: http://www.flickr.com/photos/deburca/7195447168/
License: CC BY-NC 3.0

Lawyers use indirect proof to make their cases when they lack direct evidence. If they can show that a defendant’s account contradicts the evidence, they can prove it false. Indirect proofs can be used in criminal cases, civil rights cases, and tax cases to discover the truth.

Righting Civil Wrongs

In civil rights and discrimination cases, lawyers often use indirect proof when it’s hard find direct proof of discrimination. Assume that there is no discrimination at a company. If that is true, then the firm treats all employees equally. If the firm does not treat all employees equally, then there is discrimination.

For instance, imagine a company fires a woman. She claims that she was fired because of her gender, but the company claims that she was fired because of chronic lateness. If the company does not discriminate based on gender, then men also would have been fired for being late. If men have not been fired for the same offense, then the company discriminated against the woman.

Credit: Victor1558
Source: http://www.flickr.com/photos/76029035@N02/6829438075/
License: CC BY-NC 3.0

Indirect proof can also play a part in criminal trials. For instance, in the classic American novel To Kill a Mockingbird (later turned into a film), attorney Atticus Finch points out that the accuser says his client beat her. The evidence shows she was beaten by a left-handed man. Atticus’s client, however, can only use his right hand. Therefore, he could not have beaten the woman.

See for yourself: http://www.youtube.com/watch?v=C841wEogE4U

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Read the article below and find out how indirect proof convicted a murderer.


How did indirect proof prove that the husband murdered his wife?

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Image Attributions

  1. [1]^ Credit: James Burke; Source: http://www.flickr.com/photos/deburca/7195447168/; License: CC BY-NC 3.0
  2. [2]^ Credit: Victor1558; Source: http://www.flickr.com/photos/76029035@N02/6829438075/; License: CC BY-NC 3.0

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